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Dawid Hanak's picture
Associate Professor in Energy and Process Engineering Cranfield University

I'm a climate warrior who believes that achieving our climate commitments requires immediate action. We can do this by deploying green energy technologies and building world-leading engineering...

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  • Sep 26, 2022

Humanity must remove up to 660 billion tonnes of carbon dioxide (CO₂) from the atmosphere by the end of the century to limit global warming to 1.5°C. That’s according to the most recent report by the Intergovernmental Panel on Climate Change (IPCC), which based its estimate on atmospheric CO₂ concentrations measured in 2020.

Removing this much CO₂ will involve more than simply planting lots of trees. Engineers and scientists are developing direct air capture technologies (DAC) which are supposed to pull vast quantities of CO₂ from the atmosphere while using very little land and water.

A typical DAC unit uses large fans to push air through a liquid or solid material which can bind and remove CO₂, similar to how human lungs extract oxygen. The material is regenerated when heated, leaving concentrated CO₂.

The concentrated CO₂ can either be permanently stored, usually underground in depleted oil and gas reservoirs, or used to produce useful chemicals such as synthetic fuels. These fuels would re-release CO₂ when burned and so are technically carbon neutral.

DAC technology is still in its infancy. The International Energy Agency (IEA) forecasts that it will be removing 90 million tonnes a year in 2030, 620 million tonnes in 2040 and 980 million tonnes annually in 2050.

But as things stand, only 19 DAC projects have come online since 2010, which collectively remove 0.008 million tonnes of CO₂ each year, equivalent to about seven seconds of global emissions from energy production in 2021.

DAC developers are working on projects that will remove about 1 million tonnes of CO₂ a year each in the mid-2020s. But they may struggle to improve energy efficiency and reduce costs fast enough to remove CO₂ at the necessary scale to meet the IEA’s forecasts for the 2030s.

Here’s why.

Matt Chester's picture
Matt Chester on Sep 26, 2022

The biggest issues seems to be timing. We need to be capturing carbon or shuttering the highest emitters today if we are to stay on track for 2050 goals. Can DAC provide that in the reasonable timeframe of the next few years in order to keep some of those high emitters going? 

Roger Arnold's picture
Roger Arnold on Sep 28, 2022

From the article:

Estimates suggest this method could emit 1.5 tonnes of CO₂ for each tonne removed. Although this strategy could reduce the net emissions of conventional oil production, it would still add carbon to the atmosphere.

Two points about that figure of 1.5 T of emitted CO2:

  1. It's from combustion of the amount of oil that one T of injected CO2 can be expected to recover, based on current EOR practices. But under current practices, operators purchase the CO2 they're going to inject. It's a cost item for them, and operations are tailored to achieve the maximum ratio of recovered oil to injected CO2. If their cost of CO2 for injection becomes negative (they're paid for the CO2 they inject), operations change. It pays to maximize the amount of CO2 injected, largely independent of the amount of oil recovered.
  2. The 1.5 T of CO2 emitted is from oil that would have been burned anyway, regardless of where it came from. Oil consumption is strongly demand-limited. EOR allows it to come from a well in a mature oil field, instead from a new oil field that would otherwise have had to be discovered and developed.


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